A glass fiber strand is composed of a multitude of fine glass filaments which are formed by being drawn at a high rate of speed from molten cones of glass at the tips of small orifices in a bushing such as shown in U.S. Pat. No. 2,133,238. During formation, the filaments are coated while moving at a speed on the order of 1,524 to 6,096 meters per minute with a size which contains a binder to give the strand integrity and workability for any standard textile or reinforcement use. The size also contains a lubricant for the filaments to prevent damage to the strand by abrasion of the individual filaments against each other or against handling equipment during processing.
The attenuative force supplying the high speed drawing force to form the fine glass filaments is usually provided by a winder or a wheel puller. A winder is typically a rotating drum on which a paper tube (forming tube) is placed. As the fibers are drawn and gathered into strands, the strands are collected on the forming tube which rotates with the winder. The wheel puller, as an attenuative device, is primarily a pair of tractive, juxtaposed surfaces which pull the strand and project or direct it to a collecting apparatus.
Glass fibers in the form of strand, both continuous and chopped, mat and roving having found utility in the area of reinforcing resinous matrices.
Roving is formed by mounting a plurality of glass fiber forming packages on a creel or support and gathering the strands from the separate packages in parallel, to form a rope or roving. This braided rope or roving is wound on a rotating drum to collect the roving. The roving so produced has a plurality of uses. It can be chopped and separated into separate strands to form chopped strand. It can be woven to form woven roving or it can be used by merely unwinding and impregnating it with resin for applications such as filament winding and pultrusion. Roving in whatever form utilized imparts substantial strength to resin composites reinforced therewith.
Roving which has been chopped to form chopped strand has found utility in the area of glass fiber reinforced molding compounds. In one area of glass fiber reinforced molding compounds, glass fibers which have been chopped are dispersed through a thickened, polymerizable polyester resinous material. This thickened resinous material with the glass fibers dispersed therethrough has a substantial viscosity in order that it may be handled by conventional techniques for such molding compounds.
In order to obtain a glass fiber roving which is acceptable for utilization in not only the molding compound area but also any reinforcement area the formation and processing of the roving must present as few problems in production as possible. The glass fiber strand, to form the roving must have integrity in order to tolerate the processing necessary in forming the roving and in subsequent unwinding and chopping. Also when the strands are gathered in parallel to form the roving, it is desirable that they cohere to each other to form a uniform rope. However, this adhesion between strands in the roving should not be too great because unwinding of the roving and passage of the roving through the chopping apparatus will be difficult if too much tack is imparted to the strand and the roving formed therefrom.
The strands within the roving must also be capable of being dissociated from each other during the chopping of the roving so that they may uniformly disperse throughout the molding premix.
Another problem associated with the forming of glass fibers is the migration of the binder and sizing composition when the fibers are dried after formation. The aqueous sizing composition is coated onto the fibers as they are formed and the strand, which consists of gathered fibers. The strand is then wound on a forming package. These forming packages are subsequently dried in an oven and if desired, under reduced pressure. During this drying process, the solids of the sizing composition have a tendency to migrate from the inside of the package to the outside of the package. Therefore, the strands which are on the outside of the package have substantially more sizing composition thereon than the inside strands of the package. This causes nonuniformity of the performance of the strands and roving formed from the strands. Hence, it is desirable to have a sizing composition which is nonmigratory and produces a uniform distribution of sizing composition on the strands throughout the forming package.
Along with the processing properties, the strand must also demonstrate excellent adhesion to the resin matrix to effectively reinforce the plastic article formed therefrom. Therefore both the chemical and physical properties of the glass fiber strand in the resin matrix are determined primarily by the sizing composition placed on the strand during formation.
The instant invention provides a sizing composition and a glass fiber roving formed from strand with the sizing composition thereon which is useful in the production of fiber reinforced molding compounds. Further, this invention provides composites formed from such molding compounds with improved strength and uniformity.
Further, the instant invention provides a sized glass fiber strand which is easily processed both during formation and subsequent to formation, in that the sizing composition is nonmigratory. Still further, the invention provides a strand which is easily formed into roving, is pliable, chops and disperses easily, and imparts adequate wetout and wet-through characteristics to SMC and BMC formed therefrom.
Further advantages of the instant invention will become apparent with the further description thereof.